Resistance setting device



Jan. 13, 1970 R. M R ETAL 3,490,031

RESISTANCE SETTING DEVICE Filed Aug. 28, 1967 IN vs/vroras, 41 [64 K MECUS Ffl/EOfi/CH M F440 I I I ATTORNEYS United States Patent 3,490,031 RESISTANCE SETTING DEVICE Ira R. Marcus and Friedrich W. Flad, Rockville, Md.

assignors to the United States of America as represented by the Secretary of the Army Filed Aug. 28, 1967, Ser. No. 664,240 Int. Cl. H02m 3/06 US. Cl. 32380 6 Claims ABSTRACT OF THE DISCLOSURE A resistance setting device for determining the resistive value of a parallel combination of precision resistors. The described device utilizes with each precision resistor a b1- stable resistive element the value of which is electrically altered from a high impedance to a low impedance thereby allowing current to flow through the precision resistor with which it is associated. The combination of those precision resistors conducting a current determines the resistive output of the device.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to a resistance setting devlce, and, in particular a resistance setting device utilizing bistable elements.

Briefly, our invention makes use of a new bistable resistor the value of which may be altered electrically. By so altering the resistance value of this bistable resistor a switching element such as a transistor or relay may be placed in an on or an off state. When the switching element is in an on state, current will flow through *a precision resistor, and a parallel combination of such switching elements and precision resistors will yield a given resistance value. In choosing certain ones of the switching elements in the parallel combination to be in an on state by changing the value of the appropriate bistable resistor a particular resistance value may be realized. When set to a value electrically, the bistable resistor needs no further application of power to hold it at that value.

The specific nature of the invention, as well as other aspects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings in which:

FIGURE 1 is a schematic diagram of a typical embodiment of the resistance setting device of my invention.

FIGURE 2 is a schematic diagram of a typical embodiment of means for electrically adjusting the values of the bistable resistors in the circuit of FIGURE 1.

FIGURE 3 is an alternate embodiment of the circuit shown in FIGURE 1 in which relays are used for switching purposes rather than transistors.

The bistable resistor used in my invention is similar to the one described in US. Patent No. 3,117,013 to W. R. Northove'r et al. Essentially it is an element of glass composition that may be changed from one of its two stable states to the other by an electrical signal; one of the stable states being a high impedance and the other a low impedance. When set to a stable state, the bistable resistors will retain that characteristic without further application of a signal. Generally, a change of state of the bistable resistor is accomplished by passing a specially shaped electrical pulse through it. The bistable resistor can then be reverted to its original state by passing another difierently shaped pulse through it.

In FIGURE 1 is shown a typical embodiment of my resistance setting device; this particular embodiment beice ing designed to be used in an R-C timer. It is desired to adjust the resistance between terminals 10 and 12 by placing the desired combination of precision resistors 14, 14- through 14 in parallel between terminals 10 and 12. Each precision resistor is connected to the collector of a transistor 13, 13 through 13", respectively, and is placed in circuit by rendering the transistor associated therewith conductive. That is, if transistor 13 and 13 are conducting, the resistance value between termnals 10 and 12 will be determined by the parallel combination of resistors 14 and 1.4.

Bistable resistor 11, 11', through 11 are at one end connected in common with each of the transistor emitters to terminal 10 and switch 17, and at the other end connected, respectively, in series with resistors 15, 15 through 15 which are connected to terminal 12. The junction points of bistable resistors 11, 11 through 11 and resistors 15, 15 through 15, respectively, are connected through diodes 16, 16 through 16 to the bases of the transistors 13, 13 through 13.

Assuming that bistable resistor 11 has been adjusted to its low resistance value, by the means to be described with respect to FIGURE 2, with switch 17 positioned so that the B+ voltage appears at terminal 10 and across the voltage divider consisting of resistors 11 and 15 a relatively low voltage will appear across the emitter-base junction of transistor 13 thereby not allowing the emitterbase junction to be sufficiently forward biased to permit transistor 13 to conduct. Similarly, if bistable resistor 11 has previously been adjusted to assume its high value the emitter-base junction of transistor 13 will be sufliciently forward biased to allow that transistor to conduct. When transistor 13' conducts, the value of precision resistor 14 will appear between terminals 10 and 12. Therefore the precision resistor of each stage can be made a part of the parallel combination appearing between terminals 10 and 12 by electrically adjusting the bistable resistor so that the transistor associated therewith will conduct. Diodes 16, 16 through 16 in series with the base of each transistor 13, 13 through 13", respectively, are used only to maintain the proper threshold of conduction.

In FIGURE 2 is shown the means for electrically adjusting the impedance values of the bistable resistors 11, 11' through 11 in FIGURE 1. When it is desired to electrically adjust the values of the bistable resistors and thereby alter the value of resistance between terminals 10 and 12, the setting means 22 is connected to the circuit of FIGURE 1 by connecting terminal A to terminal A, B to B through N to N, the position of switch 17 is changed to terminal G, and terminal G is connected to terminal G which is grounded.

Setting means 22 includes any conventional means for providing two differently shaped pulses to the H and L terminals, respectively, and switches 20, 20 through 20 connected to terminals A, B, through N, respectively, and which may be positioned on either a H terminal or a L terminal. The output of the H terminals provide the properly shaped pulses to set the bistable resistors associated therewith to its high resistance value, and the L terminals provide the pulses necessary to set the bistable resistors to their low resistance state. To change the resistance appearing between terminals 10 and 12 the operator chooses the proper settings of switches 20, 20' through 20 and the pulses routed through these switches to bistable resistors 11, 11 through 11 change them to the desired resistance state. The route followed by the pulse which changes the state of bistable resistor 11, for example, is from either the H or L terminal associated with switch 20, through switch 20, terminals A and A, bistable resistor 11, switch 17, terminals G and G and to ground. After each switch is set the pulses are applied simultaneously to the bistable resistors. When the precision resistor network of FIGURE 1 is put back into operation, the setting means 22 is disconnected therefrom and switch 17 is returned to B+. The setting means 22 may be used to change the states of the bistable resistors as often as required. Once electrically set, the bistable resistors will remain in the state to which they are set without the necessity of applying setting pulses to them further.

In FIGURE 3 is shown a precision resistor network similar to that of FIGURE 1 in which the switching is accomplished by relays instead of transistors. In this configuration current relays 30, 30' through 30 consisting of coils 31, 31 through 31 and armatures 32, 32 through 32 have replaced the transistors as the switching elements. Therefore, as discussed with respect to FIGURE 1 and FIGURE 2 bistable resistors 36, 36' through 36 may be set to either their high or low state to select which of the precision resistors 34, 34' through 34 are to be placed in parallel between terminals 40 and 42 to yield the desired impedance between those terminals.

While the typical embodiments described herein are designed to be used in a R-C timer, it is clear that my invention would be useful in any application where it is desired to make resistance settings by a remote means. Further, because of the bistable nature of the electrically responsive resistance elements it is apparent that devices such as those described herein have capabilities as memory circuits and digital switching circuits. Although two particular switching devices, namely transistors and current relays, have been discussed, clearly other well-known switching devices will lead themselves to this application. Of course, the circuit configuration will have to be changed in a manner appropriate to the particular switching device being used.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement Within the scope of the invention.

We claim as our invention:

1. In a variable resistance means comprising a first pair of terminals between which appears the resistance of said means, a current source and a plurality of variable resistance stages connected in parallel across said first pair of terminals, each of said stages being adapted to be connected to said current source in a predetermined relationship such that the parallel combination of those of said stages having current from said source flowing therethrough is determinative of the value of the resistance between said first pair of terminals, each of said stages comprising a precision resistor the value of which is the value of the resistance inserted by the stage in said parallel combination When current flows therethrough, one end of said resistor being connected to one of said first pair of terminals,

a normally nonconductive switching means connected to the other end of said precision resistor, to said current source and to the other of said first pair of 4 terminals, said switching means being operable, when rendered conductive, to allow current from said source to flow through said precision resistor, and

a bistable resistor having high and low resistance states and capable of being set to a predetermined one of said resistance states by an electrical impulse having a first waveform and set to the other of said resistance states by an electrical impulse having a second waveform, said bistable resistor having the further characteristic that it will remain in the resistance state to which it has been set without further application of an electrical signal, said bistable resistor being connected to said current source and said switching means in such a manner as to render said switching means operative when said bistable resistor is in one of said resistance states and inoperative when said bistable resistor is in the other of said resistance states.

2. The resistance setting means of claim 1 in which the switching means are transistors.

3. The resistance setting means of claim 1 in which the switching means are relays.

4. The resistance setting device of claim 1, comprising in addition:

(a) a plurality of second terminal means connected to each of said bistable resistors for receiving a signal capable of changing the impedance state of said bistable resistors, and

(b) a second source adapted to be connected to each of said second terminal means for providing either of two differently shaped pulses, as desired, to said bistable resistors whereby the bistable resistors are caused to change state.

5. The resistance setting device of claim 4 in which the switching means are transistors and having in addition a voltage divider means in each of said stages, said voltage divider means controlling the base-emitter voltage of said transister, said voltage divider means including said bistable resistor.

6. The resistance setting device of claim 4 in which the switching means are relays and in each of said stages said bistable resistor is connected to the coil of said relay to control the flow 0t current therethrough.

References Cited UNITED STATES PATENTS 2,858,434 10/1958 Tollefson 323-74 X 3,117,013 l/1964 Northover et al. 252-500 X 3,170,073 2/1965 Kovanic et al 307-286 3,296,521 1/ 1967 Wildberger 323- LEE T. HIX, Primary Examiner G. GOLDBERG, Assistant Examiner US. Cl. X.R. 

